In one aspect, the invention relates to columns used in liquid chromatography. In another aspect, the invention relates to introducing a sample into a chromatography column. The invention, in yet another aspect, relates to an apparatus and method for sealing the openings of vessels; in particular, the apparatus relates to sealing the openings of liquid chromatography cartridges.
Liquid chromatography is a technique for separating the individual compounds that exist in a subject sample. In employing the technique, the subject sample is carried in a liquid, called a mobile phase. The mobile phase carrying the subject sample is caused to migrate through a media, called a stationary phase. Different compounds will have differing rates of migration through the media, which effects the separation of the components in the subject sample. Liquid chromatography is commonly performed with reusable columns or with disposable cartridges, both of which are usually cylindrical, in which the media bed is bounded axially by porous plates, or plates containing defined flow paths, through which the mobile phase will flow. (See U.S. Pat. No. 4,250,035 to McDonald et al.)
Chromatography systems demand that a reliable seal be created between the column and the head through which the mobile phase enters. This is a particular problem in chromatography systems that employ disposable cartridges in which precise tolerances and careful machining that are customarily required for the creation of effective seals will increase manufacturing costs. Methods of sealing liquid chromatography cartridges typically require forcing a sealing head onto or into the cartridge. Some prior art techniques involve forcing a one-piece sealing head with an elastomeric o-ring, connected radially or to an end of the sealing head, into the cartridge. Alternately, a tapered sealing head can be forced into a cartridge without employing an o-ring to create a seal. Other prior art techniques employ o-rings or knife-edges (see U.S. Pat. No. 5,601,708 to Leavesley) oriented axially on a sealing head that create seals with the edges of the cartridges at their open ends.
Chromatography columns and cartridges also demand a close contact between the sealing heads and the media bed. Prior art sealing techniques often create gaps between the sealing head and the media bed. Even small gaps can reduce the resolution of distinct components that can be achieved. At the entrance of a column or cartridge, gaps between the sealing head and the porous plate or media will allow the subject sample to disperse and become diluted. At the exit of a column or cartridge, gaps will create a volume in which distinct fractions of the subject sample, which were separated during migration through the media, can blend back together. Thus, gaps at either end of the media bed can degrade the analytic performance of chromatography columns or cartridges.
When chemists optimize liquid chromatographic separations conditions, they may need to dissolve the sample mixture in a dissolution solvent which may be nonideal for elution. This can result in poor separation and poor recovery of desired components.
One solution to this problem is to pre-absorb the sample onto a media prior to chromatography. This involves dissolving the sample mixture in a suitable solvent and adding an amount of a dry media (usually similar to the media being used for the separation) to this solution. The dissolution solvent is then evaporated off, usually using a rotary evaporator, leaving the sample mixture dry, and absorbed to the media. The pre-absorbed media is then placed at the head of a pre-packed glass, metal or plastic chromatography column, and the optimized chromatographic solvent would flow through the pre-absorbed media and then through the column of separation media. This method has the potential hazard of the operator coming into contact with the dry powdery media both before and after the addition of the sample. This method also can lead to poor separations and recovery.
In one aspect, the invention in general relates to sealing a chromatography cartridge containing a media bed that forms a stop. The apparatus involves a sealing head that includes a first head piece, a second head piece, and an elastomeric sealing member. The first head piece includes a first compression face and a contact face adapted to contact said stop. The second head piece includes a second compression face and a compression force receiving member. The elastomeric sealing member is at least partially situated between the first and second compression faces. The first head piece, the second head piece, and the elastomeric sealing member are sized to slide easily into a chromatography cartridge having interior walls and containing a chromatography media bed that is bounded axially by porous plates.
In operation, the sealing head is inserted into the cartridge. Friction between the elastomeric sealing member and the cartridge is minimized when the elastomeric sealing member is in an uncompressed state during insertion. After the head has been inserted into the cartridge, the elastomeric sealing member is compressed between the first and second compression faces, by moving the second head piece toward the media bed so that the contact face presses against the stop. Compression of the elastomeric sealing member causes the elastomeric sealing member to expand laterally so that it presses against the interior walls of the cartridge and creates a seal.
The sealing apparatus may be removed from the cartridge by raising the second head piece relative to the first head piece, thus reducing the compression forces on the elastomeric sealing member and lessening its lateral expansion. This reduces the frictional contact between the elastomeric sealing member and the interior walls of the cartridge, so that the sealing member and the first and second head pieces may be more easily removed.
By providing a second sealing apparatus, it is possible to seal both ends of a chromatography cartridge in the manner described above.
In the preferred embodiments, the first head piece contains a body portion and an outwardly-extending shoulder. The first compression face is located on the shoulder. Additionally, the first and second head pieces are shaped and sized so that the second head piece may slidably receive the body of the first head piece. The first head piece defines a flow path for the passage of a fluid, such as a mobile phase for chromatography. The contact face on the first head piece includes a slight conical concavity that helps to distribute a mobile phase uniformly to the media bed.
In operating the preferred embodiments, the contact face of the first head piece presses against the porous plate while the elastomeric sealing member is compressed axially. This axial compression causes the elastomeric sealing member to expand laterally, thus forming a seal with the interior walls cartridge.
In another aspect, the invention in general relates to sealing chromatography columns containing a first media bed, by creating a plurality of seals. The apparatus involves a sealing head that includes a first head piece, a second head piece, an intermediate head piece, and a plurality of elastomeric sealing members. The first head piece has a body portion and a shoulder that extends farther radially than the body portion. The second head piece and the intermediate head piece define central openings through which the body portion of the first head piece is slidably fitted. The elastomeric sealing members are annular and they circumscribe the body portion of the first head piece. A first elastomeric sealing member is between the shoulder and the intermediate head piece. A second elastomeric sealing member is between the second head piece and the intermediate head piece.
The first and second head pieces, the intermediate head piece, and the elastomeric sealing members are sized to slide easily into the chromatography column.
In operation, the apparatus is inserted into the column. Friction between the elastomeric sealing members and the column is minimized when the elastomeric sealing members are in an uncompressed state during insertion. After the head has been inserted into the column, the elastomeric sealing members are compressed, by moving the first and second head pieces relative to each other, so that the second head piece moves toward the shoulder of the first head piece. The first elastomeric sealing member is compressed between the shoulder and the intermediate head piece. The second elastomeric sealing member is compressed between the intermediate head piece and the second head piece. Compression of the elastomeric sealing members causes them to expand laterally so that they press against the interior walls of the column and create seals.
In alternate preferred embodiments, an inner cartridge fits into an open end of the column. Preferably, the inner cartridge is a sample module. The sample module contains a subject sample. The sample module may also contain chromatography solvents and a chromatography media of either the same or different composition that is used in the column. The shoulder of the first head piece and the first elastomeric sealing member are sized to fit slidably into the sample module, when the first elastomeric sealing member is uncompressed. When a compressive force is applied to the sealing head, the first elastic sealing member forms a seal with the sample module and the second elastic sealing member forms a seal with the column.
Embodiments of these aspects of the invention may include one or more of the following advantages. Insertion of the sealing apparatus into a chromatography cartridge creates minimal friction between the sealing head and the interior walls of the cartridge. Use of the sealing apparatus does not require close tolerances that create a precise fit between the sealing head and the cartridge. A small amount of force is required to create a seal with chromatography cartridges, relative to prior art methods. The sealing apparatus can be easily removed from a chromatography cartridge, so that the cartridge can be replaced. Because use of the apparatus can minimize frictional shear forces during insertion into a chromatography cartridge, wear on elastomeric sealing members is reduced. Using the apparatus can create a high quality seal. Using the apparatus can minimize the gap that is created between a sealing head and the media bed or porous plate, when sealing a chromatography cartridge. Using the apparatus can axially compress the media bed while sealing a chromatography cartridge. The apparatus has the ability to create a seal by the relative motion of two pieces that compress an elastomeric sealing member without exerting axial force on the media itself. The apparatus can also create a seal by pressing the sealing head against a rigid stop within the column. The apparatus can be adapted for sealing chromatography cartridges having media beds of varying lengths and distances from the opening of the cartridge. The invention may be used with any type of column, including disposable pre-packed cartridges, columns with flexible walls, and columns made of, e.g., glass, steel, or a synthetic material. By employing a sample module that is fitted and sealed within the column a subject sample may be analyzed with two different media in one column. The sample module and the column may employ either porous plates or plates having drilled channels to bound the media beds. The outwardly extending shoulder may have any shape that allows it to exert a compressive force on an elastomeric sealing member.
In an alternative aspect, the invention features, in general, a chromatography sample module including a flow-through member having an inlet and an outlet and chromatography media within the flow-through member. A sample is added to the media, and the module, with the sample carried therein, can then be connected to a separation column.
Preferably the chromatography sample module is a tubular member that is sized to fit within the end of a chromatography column that is used for separation of the sample contained on the media in the module. Alternatively, the module can be connected to the chromatography separation column by a flow line. The sample in the dissolution solvent can be added to the sample module, and then the dissolution solvent can be evaporated. Alternatively, the sample in the dissolution solvent can be added to the sample module as a liquid without evaporation.
In yet another alternative aspect the invention features a rack of sample modules arranged in an array.
Embodiments of these aspects invention may include one or more of the following advantages. The samples can be easily introduced into separation columns. Various solvents can be used for separation and dissolution of the sample, permitting optimization of the separation procedure. Samples are easily preprocessed, and the operator is not exposed to the media before or after adding the sample. A large number of samples can be prepared for processing at one time, facilitating the carrying out of multiple separations at one time.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof and from the claims.